Windmills have been used for centuries to convert wind energy into mechanical energy. More recently wind energy has also been converted into electrical energy by windmills, generally referred to as wind turbines. While systems have been operating in several countries, in general wind energy has not played to date a significant role in meeting energy needs. With the recent energy crisis, however, and more specifically the rising cost of conventional fuels, wind energy has become more attractive.
The power available from the wind goes up as the cube of wind velocity, i.e., with double the wind velocity eight times the amount of power is available. In addition, for a given wind velocity, the power which can be extracted by a rotor varies as the square of the diameter, i.e., double the rotor diameter and four times the power is available. It is thus evident that one of the most critical components of a wind turbine is the rotor system and the economic and operational success of a wind turbine is directly linked to the overall efficiency of such rotor system. Unless the maximum power is extracted from the wind by the rotor, the entire system may not have economic viability. Consequently, aerodynamic efficiency, structural capability and reliability, enforceable control in varying wind speeds, low initial cost and long life must be inherent in its basic design.
Since, as stated above, the power which can be extracted varies as the square of the rotor, it is advantageous to increase rotor diameter as much as possible, with present and proposed designs reaching up to 200-300 ft. in diameter. At such large diameters, it is essential that loads on the rotor and the supporting structure be minimized, such as might be caused by variations in wind direction and wind velocity, and that the maximum power be extracted from the rotor at the least expense under such variable wind conditions. While such techniques as the use of yaw drive motors actuating bull gears to correct for wind direction changes and full span pitch control of the blades to correct for wind velocity variations have been reasonably successful for smaller rotor diameter wind turbines, these techniques are too costly and insensitive to be useful on wind turbines having 200-300 ft. rotor diameters.
Accordingly, it is a general object of the present invention to provide an improved wind turbine for the generation of electrical power.
It is another object of the present invention to provide a wind turbine in which fatigue-causing or excessive loads on the rotor and supporting structure can be minimized in a fast and economical manner.
It is a further object of the present invention to provide a wind turbine in which maximum power can be extracted from the wind by the rotor under variable wind conditions.